When you complete a IDPA or USPSA classifier are you limited to that same setup for competitions. For instance say I shoot the USPSA classifier with a production pistol, can I shoot a subsequent uspsa match using a single stack, in the single stack division, or do I have to stick with production.

In IDPA, you can shoot in other divisions, but you will be classified as Unclassified. Your classification is only valid for the division in which you shot it.

This does not mean you can't shoot other divisions at a local match. It is just that you will not see your score compared to people with similar skills with that type of gun.

The caveat to this are Sanctioned matches. For these, you have to be classified in the division in which you would like to shoot to compete.